Hard materials called cermets have been utilized in main bodies (substrates) of cutting tools. Cermets are sintered bodies in which hard phase particles are bonded together with an iron group metal binding phase, and are hard materials in which a Ti compound, such as titanium carbide (TiC), titanium nitride (TiN), or titanium carbonitride (TiCN), is used as hard phase particles. As compared with cemented carbide in which tungsten carbide (WC) is used in main hard phase particles, cermets have advantages, such as [1] a reduction in the amount of scarce resource W used, [2] high wear resistance, [3] a finely machined surface in steel cutting, and [4] light weight. On the other hand, cermets have problems in that they have lower strength and toughness than cemented carbide, are susceptible to thermal shock, and therefore have limited processing applications.
Hard phase particles in some cermets have a cored structure composed of a core and a peripheral portion around the core. The core is rich in TiC or TiCN, and the peripheral portion is rich in a Ti composite compound that contains Ti and another metal (such as periodic table IV, V, and/or VI group element(s)). The peripheral portion improves wettability between the hard phase particles and a binding phase, imparts good sinterability to the cermets, and thereby contributes to improved strength and toughness of the cermets. Attempts have been made to further improve the strength and toughness of cermets, for example, by controlling the composition of such a cored structure (see, for example, Patent Literature 1 to Patent Literature 4).